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    <title>7.4.JS数组-获取数组-数组新增元素</title>
    <script>
        // 1.修改length长度
        var arr = ['red', 'green', 'blue'];
        console.log(arr.length);
        arr.length = 5;     // 把数组的长度修改为5  里面应该有5个元素
        console.log(arr);
        console.log(arr[3]); // undefined
        console.log(arr[4]); // undefined
        console.log('----------------------------------');
        // 2.修改索引号
        var arr1 = ['red', 'green', 'blue'];
        arr1[3] = 'pink';
        console.log(arr1);
        arr1[4] = 'hotpink';
        console.log(arr1);
        arr1[0] = 'yellow'; // 这里是替换原来的元素
        console.log(arr1);
        arr1 = '整个替换';
        console.log(arr1); //不要直接给 数组名赋值 
    </script>
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